It is well known that designing the optical components for a spot lighting effect is in general challenging especially for light sources which are not completely uniform in their light output over angle or position. The problem becomes severe when considering medium power light emitting diodes (LEDs) for generating white light or Red-Green-Blue (RGB) LEDs for generating color variable light.
Beam shaping is found in most lighting applications. Beam shaping optical elements for example include reflectors, collimators and lenses. Such elements are used in most luminaires. All of them preform collimating and/or imaging functions.
There are many known light sources available, for example LEDs can be grouped into high power LEDs, medium power LEDs, low power LEDs, clustered LEDs and chip on boards.
The high power LEDs can be dimensionally small, for example with an area of around 1 mm2, and the phosphor of the LED can be well matched with the area of the die. This leads to a relatively uniform colored light distribution with respect to the emission angle and position within the LED emission area. These are however high cost LEDs.
Medium power and low power LEDs are often somewhat larger, for example with an area of 2-6 mm2. This often leads to color distribution effects with respect to position. Furthermore, combining such light sources with optic having some collimation characteristics can result in further color distribution effects with respect to emission angle. Conventionally, these color artifacts are solved by introducing diffusion on top of collimation in the beam shaping elements. This solution is not always possible, and when possible requires stronger initial collimation to achieve the desired beam angle, because diffusion increases the beam angle.
Thus, the color artifacts are a major issue that is well known and often obstructs the application of medium power LEDs.
Clustered LEDs are LEDs that are clustered (for example in a circle). They aim to create a more standardized light source. The advantage is that the type of LEDs can be changed without altering the source significantly (from the optical perspective). A disadvantage of clustering LEDs is that there are dark regions in between the LEDs. Combined with imaging optic the observed output produces typically bright and dark variations with respect to angle. For chip on board (COB) designs, a similar effect is observed of intensity and color artifacts in the collimated light.
Usually, a lighting company offers a range of beam angles in its spot light solutions. Philips, for example, offers at least 24° and 36° beam angles only in its professional spot luminaire range. Two different beam angle luminaires have their own dedicated optic that makes the particular beam.
EP0563874A1 discloses an optical illumination system comprising a first lens array comprising a plurality of first lenses, which are associated with a plurality of second lenses of a second lens array, arranged at focal distance of the first lens array, the second lenses mutually have different sizes and are of different size from the size of the first lenses.